Existing methods of moving aircraft controls independently from the pilot's input, for example for auto-pilot type applications, use servo actuators coupled to the primary flight control levers via linkages. Control levers may also be coupled to actuators to assist with stability of the control lever during use by a pilot.
An example of an actuator system 10 having a brake-clutch device for flight controls is shown in FIGS. 1, 2. A flight control 12, for example a joystick 14, is linked via a linkage comprising a ring 16, which surrounds an armature 18, which in turn surrounds a motor output shaft 20 which extends from a motor 22.
The ring 16 and armature 18 are coupled via a spline arrangement 23 configured such that the ring 16 and armature 18 may not rotate relative to one another, but they may slide axially relative to one another.
The armature 18 is mounted to the shaft 20 via bearing means 24. The armature 18 provides part of a brake/clutch assembly 30. Another part of the clutch 30 comprises a clutch plate 32 fixedly mounted to the end of the shaft 20. The clutch plate 32 is provided with an electromagnet and spring housing 34. Coupling means 36 in the form of interlocking teeth are provided for engagement between the plates 18, 32 of the clutch 30. A non rotatable brake/clutch stator 40, which provides an anchor, is also provided between the ring 16 and the armature 18.
In the unlikely event of a servo system failure (e.g. a “power off state”), or should the user merely want full control authority, the motor 22 is decoupled from the flight linkage, as shown in FIG. 1. The armature 18 is pushed away from the plate 32 by springs 42 located between the armature 18 and the plate 32. The same action traps the stator 40 between the armature 18 and the ring 16. This provides frictional and/or damping resistance to the movement of the ring 16, and hence the control stick 12, 14. The frictional resistance is advantageous as it allows more precise manoeuvring of the controls by the user.
Once power is restored, and as shown in FIG. 2, the electromagnet 34 is actuated and draws the armature 18 away from engagement with the stator 40, to engage with the teeth of the clutch plate 32. However, the armature 18 remains in engagement with the ring 16 by their interconnecting splines 23 to provide a drive path between the motor 22 and ring 16.
While this system works well, the magnetically operated clutch-brake device is heavy and requires considerable electrical power.
Hence an actuator which can be used for coupling and decoupling flight controls from their associated actuator, but which is inherently lighter and demands less electrical power, is highly desirable.